1. Field of the Invention
The present invention relates to an intake system for an internal combustion engine. More particularly, to an improvement in an intake system for internal combustion engine in which a partition wall for modifying the inflow characteristic of a mixture of gas supplied into an intake port to a predetermined condition is replaceably mounted in an intake port opening, and the inflow characteristic of the mixture of gas is modified from the predetermined condition to another condition, whereby the output characteristic of the internal combustion engine is appropriately regulated, thereby giving an optimum vehicle operating characteristic.
2. Description of Background Art
Hithertofore, as an intake system of a 4-stroke cycle internal combustion engine, there has been known a technology in which the inflow characteristic of a mixture of gas supplied is controlled to a special condition, thereby to achieve an enhancement in the combustion efficiency in the internal combustion engine and an improvement in the exhaust gas characteristics.
For example, Japanese Patent Laid-open No. Hei 11-166420 discloses a technology in which an intake passage on the downstream side of a throttle valve is partitioned by a partition wall into upper and lower portions as a high-load passage and a low-load passage, and at the time of low load when the opening of the throttle valve is small, the mixture of gas flows in from the low-load passage along an intake port upper wall of a cylinder head, whereby a tumble due to intake gas is generated in the cylinder, and stirring of the mixture of gas is promoted, thereby achieving stabilization of combustion and an improvement in the exhaust gas characteristics at the time of the low-load operation.
In addition, Japanese Patent Laid-open No. 2000-145467 discloses a technology in which a tumble composed of circular streams flowing in two directionalities is generated in the cylinder due to a mixture of gas and air flowing into the cylinder via an intake outlet, thereby contriving stabilization of combustion at the time of low-load operation, and the mixture of gas flows through a high-load passage and a low-load passage, whereby the mixture of gas is supplied via the intake outlet of an intake port into the cylinder in a large quantity, thereby contriving enhancement of output at the time of high-load operation.
This prior art relates to an internal combustion engine with a high intake efficiency and an enhanced output, in which the inflow characteristic of the mixture of gas is controlled to a special condition, whereby the combustion efficiency in the cylinder is improved, thereby contriving enhancement of the output characteristic of the internal combustion engine. As a result, an enhancement in the operating characteristics of the vehicle is contrived by an improvement in fuel consumption in the internal combustion engine and an improvement in the output characteristics of the engine.
Meanwhile, the operating characteristics of the vehicle vary depending on differences in operating conditions in the operating of the vehicle, even if there is no difference in the output characteristic itself of the engine of the vehicle. For example, the operating characteristics vary depending on differences in the road conditions and the rider's driving skill. Particularly, variations in the road conditions are diverse ranging from a slippery road surface at the times of rainfall, snowfall and road surface freezing to a dried-out road surface condition at the time of fine weather, and the rider's driving skill varies greatly from person to person. Thus, the operating characteristics of the vehicle vary greatly depending on variations and differences in the various conditions attendant on the operating of the vehicle. Accordingly, it is desired to develop and improve an internal combustion engine that can be changed in the specifications thereof according to the variations and differences in the various conditions in the operating of the vehicle, i.e., the road conditions, driving skill, etc.
From the viewpoint of the prior art referred to above, the development and improvement of technology according to the prior art resides in the enhancement of the operating characteristics of the vehicle that is contrived through an improvement in the output characteristic of the internal combustion engine, as described above. However, the prior art does not take into consideration the measure to cope with variations and differences in the various conditions in the operating of the vehicle.
For example, referring to the above-mentioned points from the structural features of the internal combustion engine according to the prior art, in the prior art the special control of the inflow characteristic of the mixture of gas sucked into the cylinder is performed by the partition wall provided in the intake passage as a fixed structure, the special control of the inflow characteristic of the mixture of gas is utterly invariable on a structural basis, the control of the inflow characteristic of the mixture of gas is always conducted under fixed conditions, and the regulation of the output characteristic of the internal combustion engine is conducted under fixed conditions. Thus, the specifications of the engine are not modified according to variations and differences in the various conditions in the operating of the vehicle.
Therefore, in the above-mentioned situations, it is desired to develop and improve an internal combustion engine having specifications that can be modified for coping with variations and differences in the various conditions on the operating of the vehicle, namely, various modified conditions on the operating of the vehicle. In practice, however, the development and improvement of such an internal combustion engine are difficult to achieve due to an increase in cost, and it is being desired to find a good measure to improve the internal combustion engine which makes it possible to meet the above-mentioned request by a simple structural modification and at low cost. At present, however, there has not been found any good measure to meet the above request.